It looks as though he’s spraying weeds in the garden or coating the oven with caustic cleanser. It’s not just the casual, dispassionate manner in which the University of California at Davis police officer pepper-sprays a line of passive students sitting on the ground. It’s the way the can becomes merely a tool, an implement that diminishes the humanity of the students and widens a terrifying gulf between the police and the people whom they are entrusted to protect.

The video, which shows the officer using the spray against Occupy protesters Friday, went viral over the weekend. On Sunday, the university placed two police officers on administrative leave while a task force investigates. The clip probably will be the defining imagery of the Occupy movement, rivaling in symbolic power, if not in actual violence, images from the Kent State shootings more than 40 years ago.

Although another controversial image, showing an elderly woman hit with pepper spray near an Occupy protest in Seattle, made this nonlethal form of crowd control an iconic part of the new protest movement, the UC-Davis video goes even further in crystallizing an important question: What does the social contract say about nonviolent protest, and what is the role of police in a democratic society?

Pepper spray, which in many countries is defined as a weapon and is often illegal for civilians to possess, can cause tissue damage, respiratory attacks and, in rare cases, death. It is considered far superior during crowd control to more violent forms of self-defense. But, like Tasers, which can also cause severe injury and death, there is increasing concern than it is being used by law enforcement without discretion or proper understanding of its dangers. The UC-Davis video will only amplify those concerns.

The police officer emerges from the margins of the scene, walks in front of a line of students on the ground with arms interlaced, and brandishes the can briefly in a gesture that feels both bored and theatrical, like someone on a low-budget television commercial displaying a miracle product or a magician holding the flowers he is about make disappear. He then proceeds to spray a thick stream of orange liquid into their faces. The crowd surrounding the students erupts in cries of “shame, shame,” questioning the police about whom they are protecting.

The spraying is slow and deliberate, one face after another, down the line. It is the multiple victims that makes it so chilling, recalling the mechanization of violence during the 20th century. Pepper spray, of course, isn’t meant to be lethal, and it was deployed during an effort to enforce university policy rather than a state-sanctioned campaign of violence. But the apparent absence of empathy from the police officer, applying a toxic chemical to humans as if they were garden pests, is shocking. Even more so because it is a university police officer.

University police generally operate under a more benignly paternalistic understanding of the law than other police. They are there to ensure the safety of the students, to help with the messier details of the in loco parentis function of the university.

A half-century ago, many parents told their children to ask a cop for help in case of trouble. With police forces now defining their role as more military than civilian, viewing citizens with suspicion and often treating them with hostility, that has changed. Saying the wrong thing to a cop, asking for a warrant before a search, throwing a snowball at an unmarked cop car, legally taking a picture of an official building, questioning a Capitol police officer about why a public area has been closed can lead to threats of arrest, or worse. But on university campuses, the police are often seen as they generally once were: your friend.

The UC-Davis police force has defended the use of pepper spray. An independent police expert quoted by the Associated Press calls pepper spray a “compliance technique,” in language eerily reminiscent of the George W. Bush administration’s euphemisms for torture.

Even if it is determined that the police followed proper procedures, the video might have lasting power for outrage, tapping into growing concerns not that police are abusing standard policies, but that our policies might need to be revised. Indeed, the disjunction between how the UC-Davis police read this video (they see an officer doing his job) and how many others read this video (they see a man in a uniform causing great and unnecessary pain to unresisting students) indicates that we have reached a kind of intellectual impasse about what kind of police we want and what limits should be placed on their power.

The UC-Davis video might open up a broader conversation about the proper role of the police, especially during an era in which it appears that protest against the established order may be more frequent and widespread. This new era of protest, if it continues to develop, will play out on the Internet, with rapidly uploaded videos providing not just evidence of what happens, but evidence from numerous perspectives, as each encounter is recorded by dozens of onlookers and participants.

UC-Davis has announced an investigation into the officer’s action and whether it was merited and legal. It is a familiar pattern — the video is uploaded, it spreads, outrage develops and then the institution issues a seemingly reluctant and reactive plea for caution. We don’t know the context. We don’t know what really happened.

That kind of caution grew out of an age of skepticism in response to the manipulation of photographs by unscrupulous agents, including totalitarian governments. It was an appropriate skepticism, engendering a valuable resistance to the extraordinary power of images to seem transparently truthful.

The times may be changing. Video can be as easily manipulated as photography, but multiple videos from multiple perspectives, arriving within hours or minutes after an event, require a different kind of skepticism. The repeated claims by officials that our eyes are lying begin to seem more and more incredible.